App note from Maxim Integrated on accurately measuring battery capacity by using battery monitors and fuel gauge plus software. Link here
Determining the remaining charge of a Lithium-Ion cell accurately under real world conditions requires much more than just coulomb counting. The DS2438’s integrated current accumulator (ICA) provides an accurate measurement of cell capacity under known conditions, however in applications where temperature and discharge rates vary and the cell’s capacity degrades with aging, the DS2438’s ICA needs to be adjusted to achieve the desired accuracy. This document shows how the fuel-gauging concept of the DS2438 can be expanded to insure greater accuracy under extreme operating conditions. This is accomplished by characterizing cell capacity over temperature and rate and controlling the coulomb count in software. This process is not limited to just the DS2438 or a specific type of Lithium-Ion cell. Any Maxim Battery Management device with a coulomb counter, temperature converter, and 15 bytes of user EEPROM is capable of performing high accuracy fuel gauging on any type of Lithium-Ion cell.